From the Inside Looking In : STRANGER AMONG FRIENDS. By David Mixner (Bantam: $22.95, 358 pp.)

John Balzar John Balzar is a Times national correspondent

Only sometimes does a notable life yield a worthy memoir, and this is such an instance.

David Mixner is a man of causes, a liberal political organizer and operative well-known in Los Angeles and Washington. He is a sometimes pal of Bill Clinton. He is a man of modest origins with a rather everyday complement of self-doubts, offset by uncommon certainty in what he understands to be right.

Mixner also is gay. And he has been a figure of political influence, one of the strongest links between gays and straights in the Democratic Party, through a time that was first the most exciting and euphoric in the history of American gays, then its most tragic.

Here and there along the way, Mixner also is a private man who just wants a candlelight dinner with someone special. But fear, lingering cultural taboos, a car accident, AIDS, the complexity of emerging gay relationships in a predominately straight world and once even governmental entrapment and attempted blackmail frequently leave him empty.

More times than most people could bear, Mixner has built his life, seen it fall apart and rebuilt it again.

But don't expect a maudlin story from him.

"Stranger Among Friends" is an optimist's book, the achievement of a doer. A baby boomer, Mixner has organizing skills that rise to prominence in the movement protesting the Vietnam War and his Rolodex begins to accumulate names of America's liberal elites. Here he becomes acquainted with an ambitious Clinton, uncertain about the war and its possible consequences for himself then and later.

Moving from the East Coast to California, Mixner widens his contacts to include the wealthy among the new openly gay male and lesbian community and its non-gay supporters and, ultimately, sympathetic politicians. He plays a pivotal role in organizing against a 1978 ballot proposition to ban homosexual teachers from classrooms. The campaign asked millions of Californians to rethink their views on homosexuality. They did, and gays won.

Mixner does not overlook his flops, either. And sometimes events overwhelm him and he collapses. But he doesn't search for others to blame, and extracts only momentary nourishment from self-pity. The organizer's mind propels him beyond polemics such as why. He moves ahead to ask, what can be done?

"Then came AIDS," he writes--three words that changed everything.

The fear, deathbed vigils, government paralysis, the sudden affronts from erstwhile friends, the helplessness and withering of spirit, the decline of hope and the emergence of renewed determination--AIDS stands as one of the most disturbing stories of modern America, and Mixner's account is movingly personal.

But here and throughout, Mixner as memoirist reveals himself with a tone of restraint that also distinguishes his book favorably. Any gay man with a public life knows the icy touch of the knife in the back, and he chooses not to slash back here, or at least not in a fashion discernible to the casual acquaintance.

Intimacies remain intimate, confidences do not appear to have been broken and certainly not for the sake of effect. His long relationship with his business partner Peter Scott, and Scott's romantic partner, David Quarles, is explored with a care that anyone who has tried to reduce love and anguish to words must admire--right up to the days that both Scott and Quarles fall sick and die.

Mixner concludes his book with a long account of his role in the Clinton presidential campaign, the breathless hopes of gay men and lesbians in the new president and the crushing disappointment of the administration's compromise don't-ask, don't-tell policy for homosexuals in the military. Far from a rehash, this is a freshly illuminating, elbows-flying account of constituent politics, inside and outside the White House.

Lastly, Mixner brings readers ahead to attempts by the White House, through the perseverance of staffer Marsha Scott, to repair relations with gays before this year's election--a thought not yet finished but, like Mixner's memoir, intriguing and timely.